In response to the quake, the military sent soldiers to protect nuclear sites, and the country's nuclear safety agency notified staff to be prepared in case of an environmental emergency.

China's main government Web site and a state-run newspaper described "nuclear facilities" and "radioactive sources" as including power plants, reactors, and sites for fuel production and waste disposal, as well as materials used for scientific research and medical treatment.

Thierry Charles, director of plant safety at the French watchdog group Institute for Radiological Protection and Nuclear Safety, has seen reports from the Chinese nuclear safety agency.

Charles said that materials found in the rubble appeared to come from hospitals, factories, or laboratories and were not for used for making nuclear fuel or weapons.

An unknown number of hospitals were damaged or destroyed in the earthquake. The Sichuan Province health department listed 489 major hospitals in areas that were hardest hit.

Risks Remain

Workers removing radioactive material would first find it with detection devices, then extract the material and place it in a sealed container quickly, Charles said. The material would then be repaired or disposed of as nuclear waste.

Information so far suggests "a good reaction by the Chinese teams," Charles said.

But risks remain, he noted, primarily from any materials that have not been retrieved or sealed. People who remain in close proximity could receive excessive doses of radiation.

There was also a risk that people could be exposed to radioactivity if some materials were crushed in a building collapse, he said.

Overall, Charles did not foresee a major risk to groundwater or health, because most of the material was probably metal equipment, not fuel or something that disperses more widely.

And Kristensen, of the Federation of American Scientists, said if the buried radioactive materials can be isolated and sealed quickly, there should be no risk to the public.